在Java 8中stream().map(),您可以将对象转换为其他对象。查看以下示例: 1.大写字符串列表 1.1简单的Java示例将Strings列表转换为大写。 TestJava8.java package com.mkyong.java8; import java.util.ArrayList; import java.util.Arrays; import java.util.List; import java.util.stream.Collectors; public class TestJava8 { public static void main(String[] args) { List alpha = Arrays.asList( "a" , "b" , "c" , "d" ); //Before Java8 List alphaUpper = new ArrayList<>(); for (String s : alpha) { alphaUpper.add(s.toUpperCase()); } System. out .println(alpha); //[a, b, c, d] System. out .println(alphaUpper); //[A, B, C, D] // Java 8 List collect = alpha.stream().map(String::toUpperCase).collect(Collectors.toList()); System. out .println(collect); //[A, B, C, D] // Extra, streams apply to any data type. List num = Arrays.asList(1,2,3,4,5); List collect1 = num.stream().map(n -> n * 2).collect(Collectors.toList()); System. out .println(collect1); //[2, 4, 6, 8, 10] } } 2.对象列表 - >字符串列表 2.1 name从staff对象列表中获取所有值。 Staff.java package com.mkyong.java8; import java.math.BigDecimal; public class Staff { private String name; private int age; private BigDecimal salary; //... } TestJava8.java package com.mkyong.java8; import java.math.BigDecimal; import java.util.ArrayList; import java.util.Arrays; import java.util.List; import java.util.stream.Collectors; public class TestJava8 { public static void main(String[] args) { List staff = Arrays.asList( new Staff( "mkyong" , 30, new BigDecimal(10000)), new Staff( "jack" , 27, new BigDecimal(20000)), new Staff( "lawrence" , 33, new BigDecimal(30000)) ); //Before Java 8 List result = new ArrayList<>(); for (Staff x : staff) { result.add(x.getName()); } System. out .println(result); //[mkyong, jack, lawrence] //Java 8 List collect = staff.stream().map(x -> x.getName()).collect(Collectors.toList()); System. out .println(collect); //[mkyong, jack, lawrence] } } 对象列表 - >其他对象列表 3.1此示例说明如何将staff对象列表转换为对象列表StaffPublic。 Staff.java package com.mkyong.java8; import java.math.BigDecimal; public class Staff { private String name; private int age; private BigDecimal salary; //... } StaffPublic.java package com.mkyong.java8; public class StaffPublic { private String name; private int age; private String extra; //... } 3.2 Java 8之前。 BeforeJava8.java package com.mkyong.java8; import java.math.BigDecimal; import java.util.ArrayList; import java.util.Arrays; import java.util.List; public class BeforeJava8 { public static void main(String[] args) { List staff = Arrays.asList( new Staff( "mkyong" , 30, new BigDecimal(10000)), new Staff( "jack" , 27, new BigDecimal(20000)), new Staff( "lawrence" , 33, new BigDecimal(30000)) ); List result = convertToStaffPublic(staff); System. out .println(result); } private static List convertToStaffPublic(List staff) { List result = new ArrayList<>(); for (Staff temp : staff) { StaffPublic obj = new StaffPublic(); obj.setName(temp.getName()); obj.setAge(temp.getAge()); if ( "mkyong" . equals (temp.getName())) { obj.setExtra( "this field is for mkyong only!" ); } result.add(obj); } return result; } } 输出 [ StaffPublic{name= 'mkyong' , age=30, extra= 'this field is for mkyong only!' }, StaffPublic{name= 'jack' , age=27, extra= 'null' }, StaffPublic{name= 'lawrence' , age=33, extra= 'null' } ] 1 2 3 4 5 3.3 Java 8的例子。 NowJava8.java package com.mkyong.java8; package com.hostingcompass.web.java8; import java.math.BigDecimal; import java.util.Arrays; import java.util.List; import java.util.stream.Collectors; public class NowJava8 { public static void main(String[] args) { List staff = Arrays.asList( new Staff( "mkyong" , 30, new BigDecimal(10000)), new Staff( "jack" , 27, new BigDecimal(20000)), new Staff( "lawrence" , 33, new BigDecimal(30000)) ); // convert inside the map() method directly. List result = staff.stream().map(temp -> { StaffPublic obj = new StaffPublic(); obj.setName(temp.getName()); obj.setAge(temp.getAge()); if ( "mkyong" . equals (temp.getName())) { obj.setExtra( "this field is for mkyong only!" ); } return obj; }).collect(Collectors.toList()); System. out .println(result); } } [ StaffPublic{name= 'mkyong' , age=30, extra= 'this field is for mkyong only!' }, StaffPublic{name= 'jack' , age=27, extra= 'null' }, StaffPublic{name= 'lawrence' , age=33, extra= 'null' } ] |